Yazar "Akbas, Seref Doguscan" seçeneğine göre listele

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    Application of Newmark Average Acceleration and Ritz Methods on Dynamical Analysis of Composite Beams under a Moving Load
    (Shahid Chamran Univ Ahvaz, Iran, 2022) Akbas, Seref Doguscan; Numanoglu, Hayri Metin; Akgoz, Bekir; Civalek, Omer
    In this paper, dynamic results of carbon nanotube (CNT)-reinforced composite beams under a moving load are presented. The constitutive equations in motion are obtained by the Lagrange procedure according to Timoshenko beam theory and then solved by using the Ritz method. In the solution of the moving load problem, the Newmark average acceleration method is used in the time history. In the numerical results, the effects of CNTs' volume fraction, patterns of CNTs, and the velocity of moving load on the dynamic responses of CNT-reinforced composite beam are investigated in detail. It is observed that the reinforcement patterns and volume fraction of CNTs are very effective on the behavior of the moving load. Also, it is found that X-Beam and 0Beam have the biggest and lowest rigidities in all models, respectively.
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    Dynamic Responses of Layered Viscoelastic Half-Medium with Twin Tunnel Under Harmonic Load
    (Springer Heidelberg, 2024) Yuksel, Yusuf Ziya; Akbas, Seref Doguscan
    Purpose This paper presents dynamic analysis of layered viscoelastic half medium which includes twin rectangular tunnel under harmonic load. Viscoelastic half medium is considered and modelled with using Kelvin-Voigt viscoelastic model and two dimensional (2-D) continua.Methods The considered problem is solved by using finite element method. The energy expressions of the system are obtained and equation of motion are obtained by using Lagrange procedure. Infinite region far from twin tunnel is modelled by using infinite elements with 8 nodes and finite region is modelled by using 16 nodes finite elements. The dynamic equations for finite and infinite elements are solved by using Newmark-Beta method in time domain. Finite and infinite element models with different layers and twin tunnel are generated and numerical solutions are obtained by using an algorithm by authors.Results In order to achieve verify the used models and methods, some special results are obtained and compared with results from a finite element software. In numerical studies, effects of location of twin tunnel on dynamical responses of the system under harmonic load are obtained in figures and discussed in detail. Dynamic tunnel-medium interaction is discussed in the obtained results.Conclusions The numerical results show that tunnel location plays important role on the dynamic responses of half medium and dynamic responses change significantly with tunnel-medium interaction. In field near to the tunnel, the dynamic responses are more affected. Important practical implication is that computational cost for this kind of problems could be reduced, more realistic results could be obtained and all boundary conditions could be considered by used model with infinite elements. The used model and method are very useful and practical for dynamic analysis of tunnel structures.
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    Material Nonlinear Static Analysis of Axially Functionally Graded Porous Bar Elements
    (Univ Tehran, Danishgah-I Tihran, 2024) Akbas, Seref Doguscan
    This investigation presents material nonlinear analysis of a cantilever bar element made of functionally graded material with porosity properties. The material properties of bar element are considered as changing though axial direction based on the Power -Law distribution and uniform porosity distribution. The stress -strain relation of the material is considered as a nonlinear property according to a Power -Law function. The cantilever bar element is subjected to a point load at the free end. In order to obtain more realistic solution for the nonlinear problem and axially material distribution, nonlinear finite element method is used. In the obtaining of finite element equations, the virtual work principle is used and, after linearization step, the tangent stiffness matrix and residual vector are obtained. In the nonlinear solution process, the incremental force method is implemented and, each load step, the nonlinear equations are solved by using the Newton-Raphson iteration method. In the numerical results, effects of material nonlinearity parameters, porosity coefficients, material distribution parameter and aspect ratios on nonlinear static deflections of the bar are presented and discussed. The obtained results show that the material nonlinear behaviour of the bar element is considerably affected with porosity and material graduation.
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    Nonlinear Aero-Thermo Elastic Oscillation of Inextensible Functionally Graded Beams Subject to Concentrated Harmonic Load Based on the Nonlinear Piston Theory
    (Springer Heidelberg, 2025) Alimoradzadeh, Mehdi; Akbas, Seref Doguscan
    PurposeThis paper presents nonlinear aero-thermo elastic oscillation of inextensible functionally graded (FG) beams with temperature dependent properties subject to concentrated harmonic point load with viscous aerodynamic heating by using nonlinear piston theory.MethodsGoverning nonlinear equations are derived based on Euler-Bernoulli-inextensible beam theory. Properties of FG material are considered as temperature dependent and expressed by nonlinear equation of thermoplastic material. Galerkin's method is utilized to discretize governing nonlinear partial differential equation in form of a nonlinear ordinary differential equation. Then, obtained nonlinear differential equation is solved analytically by using method of multiple time scales.ResultsNonlinear dynamic behavior of three different material constituent for FG beam includes combinations of Stainless Steel with Silicon , Stainless Steel with Zirconia and Titanium alloy with Zirconia is investigated.ConclusionsThis investigation can be helpful for mechanical analysis of structural elements under aero-thermal conditions.
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    Nonlinear Static and Dynamic Analysis of Semi-Infinite Porous Medium with Twin Tunnel
    (World Scientific Publ Co Pte Ltd, 2024) Yuksel, Yusuf Ziya; Akbas, Seref Doguscan
    Tunnel-medium interaction problems are one of the important problems in engineering. Because it has a high risk in terms of reliability, tunnel structures should be modeled in detail. The modeling of tunnel structures under static and dynamical loads is a difficult problem in engineering because of consists of a lot of conditions and effects, such as heterogeneous medium, soil layers, porosity, soil-structure interaction, groundwater, earthquake, etc. In this paper, aims to investigate the tunnel-medium interaction problems for nonlinear static and dynamic analyses. This study includes nonlinear static and dynamic analyses for layered porous semi-infinite viscoelastic medium with twin tunnels. The constitutive property of each layer of medium is considered in bilinear stress-strain relation with uniform porosity and Kelvin-Voigt viscoelastic property. The considered study is solved via the finite element method within the two-dimensional (2D) model. Layered medium is modeled as finite and infinite elements. In the solution process, the incremental force method is implemented and, for each load step, finite element equations are solved according to the bilinear stress-strain relation. In nonlinear dynamic analysis, the dynamic loads are divided by a certain finite number and applied incrementally depending on the time-dependent load function. At each load step, the final displacement, velocity and acceleration of that load step, obtained as a result of applying the Newmark beta method procedure, are assigned as the starting value of the next load step according to the bilinear stress-strain relation. Influences of porosity and position of tunnels on the nonlinear static and dynamic deflections of the system are investigated. Also, differences between linear and nonlinear responses are compared and discussed.
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    Stability Analysis of a Laminated Composite Micro scaled beam embedded in elastic medium using modified coupled stress theory
    (Univ Tehran, Danishgah-I Tihran, 2024) Akbas, Seref Doguscan
    This paper presents size dependent stability analysis a cantilever micro laminated beam embedded in elastic medium by using the modified coupled stress theory which includes the length scale parameter. The micro beam subjected to compressive load is considered as three composite laminas and embedded in elastic medium which is modelled in the Winkler foundation model. In the obtaining of the governing equations, the energy principle is used. In the solution of the buckling problem, the energy based Ritz method is implemented with algebraic polynomials. In order to accuracy obtained expressions and used method, a comparative study is performed. Many parametric studies are presented in order to investigate the buckling of laminated micro beams. For this purpose, effects of stacking sequence of laminas, geometric parameters, length scale parameter, fiber orientation angle, the parameter of elastic medium on critical buckling loads of laminated micro beams are investigated.
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    The influence of temperature on nonlinear vibration of laminated composite beams covered by FGM layers embedded on nonlinear viscoelastic foundation subjected to moving load
    (Elsevier Science Inc, 2025) Alimoradzadeh, Mehdi; Akbas, Seref Doguscan
    This investigation highlights nonlinear vibration of fiber reinforced composite laminated beams coated by functionally graded materials (FG-FRCL) resting on viscoelastic nonlinear foundation under concentrated moving load and temperature rising by von Karman nonlinearity. In solution of nonlinear dynamic problem, Galerkin method with three term approximation is implemented with using multiple time scales method to study three- to- one internal resonance. To this aim, frequency response equation of system in three-to-one internal resonance are obtained. Influences of stacking sequence, power index of the FG materials, and nonlinear parameters of foundation, temperature rising, excitation amplitude on frequency response curves of the system in three-to-one internal resonance is studied.